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In PQ News
Call of the Month for January 2026 Via the PQ Hotline, a PQ Knowledge funder requested assistance in understanding the voltagesag sensitivity of voltage-monitoring relays. Such devices are common in industrial facilities and can be a source of process interruption when voltage sags occur. The funder asked whether these devices are inherently sensitive to voltage sags and whether system robustness could be improved without compromising protection against more severe conditions such as phase loss or voltage unbalance. The facility experienced nuisance trips of medium-voltage breakers during voltage sag events, resulting in interruption of downstream process loads. Facility engineers suspected that voltage monitoring relays (VMRs) installed in the 5 kV switchgear may be overly sensitive to shortduration voltage sags and could be contributing to unnecessary breaker trips.
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EPRI Industrial PQ Training Videos
As a follow-up to our Industrial Power Quality training classes, we have posted these complementary training videos to help solidify the concepts for both utility members and their customers. The top three are listed here.
Visualizing PQ Drive Parameters for Improved Voltage Sag Ride-Through 
This video demonstrates the voltage sag susceptibility of AC drive systems and how to improve the drive’s robustness through parameter changes.
Understanding PLC Voltage Sag Ride-through: AC and DC Powered Systems
This video demonstrates the differences in voltage sag ride-through between an AC powered PLC system and a DC Powered PLC system.
Power Conditioning to Enhance Control System Voltage Sag Ride-Through: The Constant-Voltage Transformer
This video shows how a CVT can be utilized to harden the voltage sag response of an automated control system.